This invention relates to the manufacture of mats, rugs and carpets, particularly mats, rugs and carpets where a rubber (natural or synthetic) backing sheet is cured and heat-bonded under pressure to the back of a fabric layer leaving a rubber border extending beyond the fabric layer. It also relates to mats, rugs and carpets as such and to apparatus for use in producing them.
The invention is of particular utility in the manufacture of washable mats, rugs and carpets such as dust-control mats. The term xe2x80x9cwashablexe2x80x9d means washable by immersion and agitation in water or other cleaning fluid usually followed by spin extraction and tumble drying. The term xe2x80x9cmatxe2x80x9d is used hereinafter in a wide sense to include rugs and carpets.
Dust control mats have conventionally been made by first laying down an uncured sheet of rubber, placing a mat fabric layer on top of it leaving the required border (e.g. 2 cm), and placing the assembly of the two layers in a heated press which cures the rubber and bonds it to the fabric. The layers are conveniently assembled on a horizontally movable carrier which can be moved into and out of the press on rollers, the carrier having an upper layer of flexible material secured around its edges to form an inflatable bag. Once in the press the carrier can be raised with hydraulic or pneumatic rams beyond a point where support blocks can be moved horizontally beneath the carrier (so that the rams do not sustain the pressing force). The bag is then inflated to press the mat assembly against a heated platen disposed above it and heated to say 170xc2x0 C. by pressurised steam in conduits in the platen. The advantage of applying pressure using a bag is that a bag conforms to the contour of the mat assembly and applies an even pressure. After curing the pressurised air in the bag is released and the bag evacuated by applying suction or using the hydraulic or pneumatic rams to squeeze the air out. The support blocks are removed and the rams lower the carrier so that it can be removed from the press.
This arrangement is generally preferred as the operator can easily locate the fabric layer on the backing layer when the fabric layer is on top and it is desirable to apply the heat from the fabric side so as to ensure proper bounding of the two layers so that they do not separate in use. However it is possible to reverse the arrangement so that heat is applied to the rubber side and/or the fabric layer is beneath the rubber layer. Also, if the range of movement of the bag surface is sufficient, it is possible to omit the rams and the blocks because the assembly is sufficiently close to the heated platen when it enters the press.
It is conventional to provide release sheets of non-stick material such as polytetrafluoroethylene or silicone materials between the fabric layer and the platen and between the bag and the rubber. It is also conventional to provide a light aluminum (or other metal) moulding sheet in contact with the rubber, the moulding sheet having holes or depressions which mould projections (cleats) or patterns (e.g. logos) into the rubber. Silicone rubber moulding sheets can also be used.
The rubber flows outwardly during pressing to form edges which taper down to a very small thinness. These edges are prone to tearing and extend by unpredictable distances. Hence it is necessary in practice to trim the cured backing sheet with guillotines or knives. Finally it is conventional to provide small openings in the rubber backing to allow passage of water during laundering, particularly during spin extraction. This can be achieved by running the mats between a spiked roller and a backing roller having grooves aligned with the spikes.
The three steps of (a) assembling the layers and operating the press, (b) trimming the edges of the backing, and (c) piercing the backing, are labour-intensive and we have sought ways of improving the efficiency of the overall process.
According to the invention, we provide a process for making a mat (preferably a dust control mat) having a fabric layer and a rubber backing layer using a press which heat-cures the rubber and adheres it to the fabric and employs an inflatable bag to apply pressure by pressing the layers against a heated platen, wherein a frame defining the extent of the periphery of the mat is located between the bag and the platen and wherein the bag applies pressure over substantially the whole area of the backing layer.
According to a preferred embodiment of the invention, we provide a process for making a mat (preferably a dust control mat) having a fabric layer and a rubber backing layer with a border extending beyond the fabric layer using a press which heat-cures the rubber and adheres it to the fabric and employs an inflatable bag to apply pressure by pressing the layers against a heated platen, wherein a frame defining the extent of the border is located between the bag and the platen, and wherein the bag applies pressure to the assembled layers including the border portion of the backing layer. A border beyond the fabric layer is normally provided but the invention is operable without any border or with a very small border e.g. 1-2 mm wide if the frame cannot cut through the fabric layer; for convenience only, the following description refers to mats with borders.
Preferably, rubber accumulates in the areas immediately inward of the frame while it is still flowable such that a thickened reinforcement is provided in these areas of the cured backing layer. Thus, according to another aspect of the invention, we provide a mat in which a rubber backing sheet has an integral thickened peripheral region.
Preferably the bag applies pressure to the fabric side of the assembled layers although the alternative arrangement where it applies pressure to the backing side can be used.
The press may take a number of forms e.g. as described in U.S. Pat. No. 4,447,201 to Knudsen, the contents of which are incorporated herein by reference. This patent describes the more common movable frame type of press. However, fixed frame presses such as that described in EP-A-367441 may be used. A number of presses suitable for making dust control mats are commercially available from Shaw-Almex USA Inc. of 3529-H Church Street, Clarkston, Ga. 30021, USA.
The frame is normally of metal and in one preferred arrangement, can for example be part of (formed e.g. by machining, moulding or casting) or connected to (e.g. adhered to or welded to) the moulding sheet referred to above. Thus, according to a further aspect of the invention, we provide a moulding sheet for use in making mats by heat-compression moulding an assembly of a rubber backing layer and a fabric layer, the sheet comprising or being associated with a frame defining the mat periphery.
The frame can be greater or smaller in area than the initial area of the backing layer. If it is greater in area than the initial area of the backing layer it acts as a dam; if it is smaller it acts both as a guillotine and a dam. The latter arrangement is preferred in which case the frame needs to have a cross-section which is narrow at the top or bottom to provide a cutting action.
In order that the operator can ensure that the border is in the correct position, another preferred arrangement is for the fabric layer and for the frame (which in this case is separate from the moulding sheet) to be both placed on top of the backing layer such that in the press the bag bears down on both the fabric layer and the frame, the latter being forced downwardly through the backing layer.
It is preferred to make the frame of metal rod, particularly of circular section with the section diameter being preferably about twice the backing layer thickness in the central part of the finished mat. If the diameter (height) is too small, the thickened rubber layer in the border may be too thin; if it is too great, the inherent stiffness of the bag material may prevent adequate compression in the angle between the frame and the top of the backing layer. A circular section rod may provide a concave end to the border but this has been found not to be a disadvantage. A circular section rod of appropriate diameter is sharp enough to be pushed through the rubber, during initial operation of the press, while being blunt enough to avoid damage to the bag.
Normally the finished mat will be rectangular and a rectangular frame will be used. However, other shapes such as circular or rectangular with rounded corners can be used. Also, the sides of the frame will not necessarily be joined together but this will normally be the case so that unwanted movement during pressing is avoided. Thus the frame may be interrupted and define only part of the mat periphery e.g. one or more sides of the frame may be omitted.
It will be seen that the process described eliminates a subsequent trimming operation since any excess rubber outside the frame can be peeled away after pressing. It is also possible, according to a preferred feature of the invention, to simultaneously pierce the backing to provide the small holes described above. This can be achieved for example by providing spikes on the moulding sheet referred to above. The spikes need not necessarily pass completely through the backing since a thin membrane at the end of the hole which they provide will be broken during subsequent use of the mat. The moulding sheet may be shaped to provide dish-like depressions around the holes as described in our GB patent application GB-A-2275869.
As mentioned above, a further advantage of the invention arises from accumulation of rubber in the border area where the maximum strength of the backing layer is required. This means that the thickness over the main area of the mat can be reduced e.g. from 2 mm to 1 mm because the accumulation in the border area can double the thickness. This of course means that the amount of rubber used is substantially reduced. Also the use of a frame reduces wastage simply because there is no longer a substantial tapered peripheral area of backing layer which has to be trimmed off to achieve the desired edge thickness.
Instead of using a greater overall thickness to achieve the required border thickness, some previous mats have a reinforced border made by heat fusing an extra layer of rubber thereon. This is labour-intensive and can lead to rippling due to differential shrinkage of the two rubbers during laundering. The present invention can be used to overcome these disadvantages.